Where the two pieces of intake pipe join, is that a valve or just a coupling? If it's a valve, is it a one-way check valve? And if it is a valve, has anyone tried removing it in favor of just a hose coupling?

Ahhh...Air Bypass Valve to prevent hydrolock.

Ahhh...Air Bypass Valve to prevent hydrolock.
Yup that's what it is, and another reason it costs so much.

that is something you can buy and add to another intake.

Where the two pieces of intake pipe join, is that a valve or just a coupling? If it's a valve, is it a one-way check valve? And if it is a valve, has anyone tried removing it in favor of just a hose coupling?

I have used both. I would stay with the bypass valve. I mean its bs enough driving in CA with drunk drivers, flash floods, earthquakes, police chases, pedestrians, 405 traffic etc. for me to also worry about ingesting water into the motor.